JP2010182995A - Shield device for signal amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve suppression effect on intermodulation with respect to a shield device for a signal amplifier. <P>SOLUTION: Shield materials 21 are added on an internal surface of a case 22 containing a signal amplifier circuit 10, and each of the shield materials 21 is formed by laminating an insulating film 21a, a metal foil 21b, and a protective film 21c. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a shield device for a signal amplifier that can be suitably applied to a high-frequency amplifier for TV signals, for example.

  In a signal amplifier that inputs two or more signals, a shielding technique has been proposed for mitigating intermodulation caused by third-order distortion of a nonlinear element (Patent Document 1).

  That is, when an adjustment hole such as a volume is opened in the shielding case of the signal amplifier, radio waves from the antenna on the output side may enter the amplifier circuit through the adjustment hole and cause intermodulation. Therefore, the intermodulation can be suppressed by mechanically closing these adjustment holes.

JP-A-8-279687

  In the case of such a conventional technique, there is a problem in that the effect of suppressing intermodulation is not always sufficient because only the adjustment hole opened in the shielding case is focused.

  Accordingly, an object of the present invention is to provide a signal amplifier shielding device that can realize a better intermodulation suppressing effect by attaching a shielding material to the inner surface of the case in view of the problems of the prior art. There is.

  In order to achieve this object, the structure of the present invention has a shield material attached to the inner surface of the case that houses the signal amplifier circuit, and the shield material is made of an ungrounded metal foil on an insulating film that is in contact with the inner surface of the case. The gist is to laminate.

  In addition, a protective film can be laminated | stacked on metal foil.

  According to the configuration of the invention, by providing a shield material on the inner surface of the case, it is possible to effectively suppress the intermodulation distortion generated on the output side of the signal amplifier, particularly the third-order intermodulation distortion due to two signals. it can. However, the shielding material is a non-grounded metal foil laminated on an insulating film that adheres closely to the inner surface of the case, and a uniform capacitor is formed on the inner surface of the case by the metal case, the insulating film, and the metal foil. It shall be.

  If a protective film is provided on the metal foil, there is no possibility that the object will hit and the metal foil will be damaged, or the potential of the metal foil will not be inadvertently changed.

Overall configuration longitudinal section The main part expansion schematic exploded view of FIG. Test result data table Test condition table Overall block diagram showing test circuit Explanation of output waveform of test results FIG. 1 equivalent view showing another embodiment

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The shield device of the signal amplifier is formed by attaching shield materials 21, 21... To the inner surface of a shielding case 22 that houses the signal amplifier circuit 10 (FIG. 1).

  The signal amplifier circuit 10 is mounted on the substrate 11a and is fixed to the bottom surface of the case 22 via set screws 11b and 11b. An input side and an output side of the signal amplifier circuit 10 are led out to an input terminal T1 and an output terminal T2 outside the case 22 via shielded cables 11c and 11d, respectively. The case 22 is a metal case having a shielding function, and is formed in a sealed box shape as a whole.

  The shield material 21 on the inner surface of the case 22 is configured by laminating an insulating film 21a that is in close contact with the inner surface of the case 22, an intermediate metal foil 21b, and a protective film 21c on the metal foil 21b (FIGS. 1 and 2). . The insulating film 21a and the protective film 21c are single-layer or multi-layer plastic films each having a thickness of about several tens to several hundreds of micrometers. The metal foil 21b is, for example, a foil made of Al, Sn, Cu or the like having a thickness of about 10 μm, and is laminated so as to be sandwiched between the insulating film 21a and the protective film 21c without being grounded. The insulating film 21a and the protective film 21c are the same size as each other and slightly larger than the metal foil 21b, but may be substantially the same size as the metal foil 21b. In addition, it is preferable that the shield materials 21, 21...

  An example of a test result of such a signal amplifier shield device is shown in FIGS. However, the test result data of FIG. 3 is measurement data by the test conditions of FIG. 4 and the test circuit of FIG. 5, and FIG. 6 is an output waveform diagram of the test circuit of FIG. 5 and a schematic diagram for explanation thereof. .

  In FIG. 5, with respect to the signal amplifying circuit 10 in the case 22 of FIG. 1, the levels of the two signals of the frequencies f1 and f2 from the signal generator 31 are made the same and applied to the input terminal T1, and the output signal from the output terminal T2 Is guided to the pseudo antenna 33 through the directional coupling unit 32, and the branch output from the directional coupling unit 32 is connected to the spectrum analyzer 34 through an attenuator (not shown). The signal amplifying circuit 10 has an IF amplifier 12, a converting unit 13, and a power amplifying unit 14 cascaded between an input terminal T1 and an output terminal T2, and an output of the oscillating unit 15 having a frequency fo through the amplifying unit 16. Are connected to the conversion unit 13. Note that f1 = 21.33 MHz, f2 = 22.26 MHz, fo = 705.5 MHz, and the output of the power amplifier 14 is 0.5 W. However, the signal amplifying circuit 10 included in the case 22 of the test used a 30UT-77 type transmitter manufactured by Mitsubishi Electric Corporation for television broadcasting.

  In FIG. 3, before the countermeasure, the shield materials 21, 21... Are not attached to the inner surface of the case 22 at all, and the countermeasures 1 to 3 are the shield materials 21, 21. Is attached. However, the contents of measures 1 to 3 are as shown in FIG. That is, in measures 1 to 3, the insulating film 21a and the protective film 21c are laminated films of polyethylene terephthalate (PET), low density polyethylene (LDPE), and ethylene vinyl acetate copolymer resin (EVA) that are commercially available as laminate films, respectively. The total thickness of the insulating film 21a was set to 100 μm, 300 μm, and 500 μm while maintaining the total thickness of the protective film 21c at 100 μm. The metal foil 21b was an Al foil having a thickness of 11 μm through measures 1 to 3. In addition, the measured value of the capacity | capacitance of the capacitor | condenser which sandwiches the insulating film 21a and uses the metal foil 21b and the inner surface of the case 22 as an electrode is shown together in FIG.

  6A to 6D show the output waveforms of the test circuit of FIG. In each output waveform, the horizontal axis is the frequency, the vertical axis is the level (dBμV), and the two waves at the center are the frequencies F1 = f1 + fo = 726.83 MHz and F2 = f2 + fo = 727.76 MHz. It is a fundamental wave. A pair of i-order intermodulation distortions IMi, IMi (i = 3, 5, 7,...) Are sequentially arranged on both outer sides of the central two waves (see FIG. 6E). However, the i-th order intermodulation distortions IMi and IMi are generated at both frequency intervals F2 -F1 = 0.93 MHz on both outer sides of the two fundamental waves. In addition, each pair of i-order intermodulation distortions IMi and IMi on both outer sides of the two fundamental waves are substantially at the same level. Therefore, FIG. 3 shows an average of the levels of the pair of i-order intermodulation distortions IMi and IMi on the outer sides with the level of two fundamental waves as a reference level.

  According to FIG. 3, it can be seen that measures 1 to 3 have a significant deterrent effect on the third-level intermodulation distortion IM3 at the second highest level after the fundamental wave. However, if the insulating film 21a is thickened to 300 μm or more to reduce the capacitance of the shield material 21 as a capacitor, the higher-order intermodulation distortion after the fifth-order intermodulation distortion IM5 tends to deteriorate. Therefore, it is preferable that the thickness of the insulating film 21a is appropriately adjusted and set according to the required frequency characteristics.

  Since the protective film 21c is for protecting the metal foil 21b, the metal film 21b is preferably sandwiched between the insulating film 21a and thermally bonded. However, since the protective film 21c hardly contributes to the effect of suppressing intermodulation distortion, it may be omitted.

Other embodiments

  The case 22 can be provided with shield materials 21, 21... On the inner surface of each chamber that individually accommodates the signal amplifier circuits 10 and 10 that are connected in cascade (FIG. 7).

  In the figure, the shield material 21 is also attached to the bottom surface of each chamber of the case 22. The shield cables 11c and 11d on the input terminal T1 side and the output terminal T2 side are respectively provided with a shield material 23 similar to the shield material 21 on the outer periphery. The same applies to the shielded cable 11e that connects the signal amplifier circuits 10 and 10. The shield member 23 can be configured by applying a metal foil or a metal braid on the outer peripheral insulating sheath of the braided shield of the shield cables 11c, 11d, and 11e, and providing a protective insulating outer shell on the outer periphery.

  It should be noted that the present invention is preferably used in combination with any other intermodulation or cross modulation suppression countermeasure means such as a bypass capacitor provided in the power supply circuit of the signal amplifier circuit 10.

  The present invention can be widely applied to a wide-band high-frequency amplifier for all uses as a countermeasure against intermodulation.

DESCRIPTION OF SYMBOLS 10 ... Signal amplification circuit 21 ... Shield material 21a ... Insulating film 21b ... Metal foil 21c ... Protective film 22 ... Case

Patent applicant Kyuichi Ose
Attorney Tadaaki Matsuda, Attorney

Claims (2)

  A shield for a signal amplifier, characterized in that a shield material is attached to the inner surface of a case for housing a signal amplifier circuit, and the shield material is formed by laminating a non-ground metal foil on an insulating film in contact with the inner surface of the case. apparatus.   2. The signal amplifier shield device according to claim 1, wherein a protective film is laminated on the metal foil.

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